Digital three-dimensional object manufacturing, also known as digital additive object manufacturing, is a process of making a three-dimensional solid object of virtually any shape from a digital model. Three-dimensional object printing is an additive process in which one or more ejector heads eject successive layers of material on a substrate in different shapes. Typically, ejector heads, which are similar to printheads in document printers, include an array of ejectors that are coupled to a different source of material. Ejectors within a single ejector head can be coupled to different sources of material or each ejector head can be coupled to different sources of material to enable all of the ejectors in an ejector head to eject drops of the same material. Materials that become part of the object being produced are called build materials, while materials that are used to provide structural support for object formation, but are later removed from the object are known as support materials. Three-dimensional object printing is distinguishable from traditional object-forming techniques, which mostly rely on the removal of material from a work piece by a subtractive process, such as cutting or drilling.
A previously known three-dimensional object printing system 10 is shown in FIG. 8. In the view depicted in that figure, a platform 14, called a cart, includes surfaces 18 (FIG. 7) that slide upon track rails 22 to enable the cart to move in a process direction P between printing stations, such as the printing station 26 shown in FIG. 8. Alternatively, carts can include wheels configured to roll along tracks, or other types of acceptable mobility mechanisms. Printing station 26 includes four ejector heads 30 as shown in the figure, although fewer or more ejector heads can be used in a printing station. Once the cart 14 reaches the printing station 26, the cart 14 transitions to and moves along precision rails 38 through the printing station. Precision rails 38 are cylindrical rail sections that are manufactured within tight tolerances to help ensure accurate placement and maneuvering of the cart 14 beneath the ejector heads 30. Linear electrical motors are provided within housing 42 to interact with a magnet inside housing 46, which is connected to the lower surface of the cart 14. The motors generate electromagnetic fields that interact with the magnet to propel the cart along the track rails 22 between print stations and along the precision rails 38 within the printing stations. Once the cart 14 is beneath the printing station 26, ejection of material occurs in synchronization with the motion of the cart. Electrical motors (not shown) are operatively connected to a gantry to which the ejector heads are mounted to move the ejector heads in an X-Y plane that is parallel to an upper surface of the cart 14 and perpendicular to the motion of the cart down the track or rail as layers of material are formed in the object. Additional motors (not shown) move the printing station 26 vertically with respect to the cart 14 as layers of material accumulate to form an object. Alternatively, a mechanism can be provided to move an upper surface of the cart 14 vertically and horizontally for formation of the object. Once the printing to be performed by a printing station is finished, the cart 14 is moved to another printing station for further part formation, layer curing, or other processing.
An end view of the system 10 is shown in FIG. 7. That view depicts in more detail the surfaces 18 that rest upon the rails 22 that extend from and above the electrical motor housing 42. As the motors generate electromagnetic fields that interact with the magnet in housing 46, the surfaces 18 of the cart 14 slide along the track rails 22. At the printing station, the bearings 34 of the cart 14 contact the precision rails 38 in an arrangement that facilitates accurate positioning of the build platen on the cart 14. Specifically, bearings 34 are positioned at a right angle to one another on one of the rails 38 to remove four degrees of freedom of the cart 14, while the other bearing 34 rests on the other rail 38 to remove one more degree of freedom. Gravity and magnetic attraction between the electrical motor and the magnet in the housing 46 hold the bearings 34 in contact with the rails 38.
When carts are not present underneath the ejector heads 30, errant drops of materials can fall from the ejector heads and produce undesired debris and contamination on the precision rails 34 and the housing 42. Contaminants can become hardened in the presence of ultra-violet radiation, which may be used during a curing process in the printing system 10 or by cooling in the case of thermoplastic materials. This can lead to a continual buildup of a layer of contaminating material. Other materials such as particulates and other stray matter can also accumulate on the rails 34 or other portions of the printing system 10 and interfere with a printing operation.
In order to produce three-dimensional objects with acceptable quality, the motion of the cart 14 beneath the ejector heads 30 needs to be precise. If materials from the ejector heads collect where the bearings 34 interface with the precision rails 38, the linear velocity of the cart 14 is disrupted and the quality of the printed object is affected. Additionally, the collection of material drops on top of the housing 42 may affect the dissipation of heat from the motors and impact the performance and reliability of the motors. Therefore, improvements in three-dimensional object printing systems that mitigate the risk of contamination on the precision rails, motor housing, and mobile cart would be beneficial.